Unlock foreman|thin gems, and upgrade.
Upgrade gems.

Hold ActiveAdmin back at v0.5.1, because upgrading to v0.6.0 causes
failures.
Merge branch 'upgrades' into develop
Build Travis for Ruby >= 1.9.2.

Include Redis and PostgreSQL services, configuring RSpec test script
to use test `DATABASE_URL`.
Adjust Travis build to migrate database and use bundle exec.

Note that `db:test:prepare` is not suitable, because of the ActiveAdmin
information embedded within the migrations.
Add empty config/database.yml, which should not be used.

For some reason, `rake db:migrate` appears to fail if there is no
`config/database.yml`, even with `DATABASE_URL` set (which it goes on
to use).
Install database_cleaner, using for testing.

The `use_transactional_fixtures` config for RSpec doesn't appear to
roll back transactions correctly, causing tests to fail. Use
`database_cleaner` transactions, instead.
Document Travis build status in README.
Bump version to v1.3.1.
Merge branch 'release/v1.3.1'